The Geological History

When, 120 million years ago, the first Cretaceous materials of Costa Quebrada were first deposited, they were in the warm and clean water of the Tethys Sea. Meanwhile, reptiles dominated the living world in the far-off emerged lands. However, large reefs were developed here under the clean water, made up of certain molluscs, the rudists, and some corals.

As these reefs became larger, voluminous masses of Aptian Cretaceous limestone rock were formed. Nowadays, once emerged, they arise as significant rock masses along the La Marina and the limestone massifs east of the river Miera. Their mining potential has always been of great interest in Cantabria. This is confirmed by the mining activity carried out at Cabárceno, Reocín, Puerto Calderón, and the countless quarries of Camargo and Eastern Cantabria.

But nothing lasts forever in the long history of our planet and, after five million years, the placid waters were disturbed by a change in rainfall patterns and the sea level.

During the Albian, 112 million years ago, sediments transported by the rivers coming from the south and the west buried the rudists and corals and thus hindered their survival here. Initially, only the finest sediments (silt and clay) arrived. They were loaded with plant debris, wood from forests and small resin fragments. Ancient insects have been found in some of these resin fragments (amber), elsewhere in the basin.

The dark silts filled the basin as they became thicker, resulting in coastline advance. Near the coastline, the sandbars of a vast beach were deposited, burying the silts. However, the sea level rose on several occasions and, with each rise, the dark silts buried the sands once again, accumulating in thick layers until they filled the basin and the sands returned.

The siltstones and sandstones found today at the isthmus of Somocueva were formed this way. They can be found along the central coastline of Cantabria, too, from Suances to Comillas and the inner valley of the river Nansa.

These silt / sand cycles were not exactly alike. Over time, each new sand deposit contained more calcium. Consequently, the sand deposit would gradually become a new limestone deposit, where the many marine organisms that died would remain, trapped and fossilised. Ammonites, sea urchins, sea snails, corals, sponges, and many other organisms were part of rich marine communities.

The limestone sank slowly into the basin until the deposition stopped. Furthermore, the quantity of dissolved oxygen in the sea experienced a substantial decrease at the end of this process, which led to an important mass extinction of marine species.

This way, a layer of ochre coloured limestones originated, the same renowned Cenomanian limestones that our ancestors used to paint their beliefs and their world in Altamira.

The inert reef, which was now deep in the waters of a colder, poorer sea, was then buried by new sediments. The almost lifeless clays burst onto the scene.

As they were being deposited, the climate didn’t remain the same. Periods of tens or hundreds of thousands of years of warm, humid weather were followed by long periods of cold, dry weather. These fluctuations determined the type of sediments that would reach the basin.

During long years, copious rainfalls would load the basin with clays, whereas in other times, clays were less abundant and shell and calcium-rich debris deposition would predominate.  This calcium cemented the clays when it was most abundant, originating more resistant alternating layers. Irregular sea urchins, corals, sponges, ammonites, bryozoans and many other organisms lived in this environment.

This cyclic process took place countless times from the Turonian to the Santonian, creating the series of thin layers of marlstone and gray limestone found along the cliffs of eastern Costa Quebrada.

From the Maastrichtian onwards, about 70 million years ago, this little basin began to rise, slowly. Consequently, sands gradually became present again, along with the influence of currents. The sandy limestones found between Covachos and San Juan de La Canal were deposited in this environment.

This was the case until the end of the Mesozoic, 65 million years ago. With the mass extinction that put an end to the dominance of large reptiles, many other creatures also became extinct. At that time, sandy materials became exposed to the elements, in the middle of some coastal brackish lagoons. Certain very soluble rocks were deposited there-the dolomites of the cove of La Canal.

The coastal environment of the sandy deposits, constantly movilised by currents and waves, fostered the formation of the most recent materials of Costa Quebrada-the calcarenites and limestones found near the island of Virgen del Mar. Numerous sea urchins, annelids and sponges lived in this hectic environment.

Already at that time, the collision between the African and the European continents began. The Iberian island was compressed against Europe, causing the uplift of all the mountain ranges in southern Europe: the Cantabrian Range, the Pyrenees, the Alps, the Balkans and the Carpathians.